Objectives : The purpose of this study was to examine the changes in metabolic parameters and Positive and Negative Syndrome Scale (PANSS) scores of patients previously treated with atypical antipsychotic drugs other than paliperidone, after 8 weeks of treatment with paliperidone. Methods : Changes in body weight, body mass index, leptin, lipid levels, fasting glucose, and PANSS scores of patients who switched from other atypical antipsychotic drugs to paliperidone were measured after 8 weeks of treatment with paliperidone. We compared these results with those of patients who had not been treated with antipsychotic drugs for at least 2 weeks prior to treatment with paliperidone (antipsychotic drug-free patients). Results : The antipsychotic drug-free group (n = 9) did not show significant changes in metabolic parameters, but showed a significant improvement in total and subscale scores of PANSS. In the group that switched from other atypical antipsychotic drugs to paliperidone (n = 13), body weight, body mass index and fasting glucose level significantly increased, while total and subscale scores of PANSS significantly improved. Conclusions : Paliperidone treatment will benefit patients with schizophrenia who have been antipsychotic drug-free or who have had difficulty with other atypical antipsychotic drugs, with regard to their psychopathological state. However, if patients have been treated with other atypical antipsychotic drugs before switching to paliperidone, they could gain body weight or their fasting glucose level could increase over a short period because of a change in receptor number and sensitivity caused by the previously prescribed antipsychotic drugs, and hence, paliperidone should be prescribed with caution for these patients.